Siei-jong, who succeeded to the throne on the death of his father, Hetai-jong, enjoyed a long reign of thirty-two years, during which the fortifications of the capital were added to and strengthened. The Manchius beyond the Ever-white Mountains were then beginning to rise in power, and Liao Tung was disturbed by the raids of tribes from Mongolia, which the Ming generals were unable to suppress. When the fighting took place within fifty miles of her own boundary river, Chō-sen became alarmed, and looked to the defence of her own frontier and capital. In 1450, on the death of the king, who “in time of peace prepared for war,” Mun-jong, his son, succeeded to royal power. As usual on the accession of a new sovereign, a Chinese ambassador was despatched from Peking, which had been the Ming capital since 1614, to Seoul, to confer the imperial patent of investiture. This dignitary, on his return, wrote a book recounting his travels, under the title of “Memorandum concerning the Affairs of Chō-sen.” According to this writer, the military frontier of Corea at that time was at the Eastern Mountain Barrier, a few miles northwest of the present Border Gate. Palladius, the Russian writer, also states that, during the Ming dynasty, three grades of fortresses were erected on the territory between the Great Wall and the Yalu River, “to guard against the attacks of the Coreans.” It is more in accordance with the facts to suppose that the Chinese erected these fortifications to guard against invasion from the Manchius and other northern tribes that were ravaging Liao Tung, rather than against the Coreans. These defences did not avail to keep back the invasion which came a generation or two later, and “the Corean frontier,” which the Chinese traveller, in 1450, found much further west than even the present “wall of stakes,” shows that the neutral territory was then already established, and larger than it now is. Of this strip of rich forest and ginseng land, with many well-watered and arable valleys, once cultivated and populous, but since the fifteenth century desolate, we shall hear again. In Chinese atlases the space is blank, with not one village marked where, until the removal by the Chinese government of the inhabitants westward, there was a population of 300,000 souls. The depopulation of this large area of fertile soil was simply a Chinese measure of military necessity, which compelled her friendly ally Chō-sen, for her own safety, to post sentinels as far west of her boundary river as the Eastern Mountain Barrier, described by the imperial envoy in 1450.